so im building a sumo bot an i thought that the best sensors that can be used for detecting opponents would be an ir receiver (http://robotgestation.com/images/Sensor-VisharIRRemote.gif), so i hooked up gnd to gnd and "V" to 5 v source, and the signal pin to a multimeter, to measure voltage, but the problem is that the receiver is too sensitive i want it to detect objects when ir light is reflected by the object but even if i turn on the ir led next to it from 5.00 reading it goes to 4.5v . and when a object comes in front of the sensor it shows the same output of 4.5 v.

You need to shroud the receiver (and possibly/probably the IR LED), either in a tube or behind a block with a hole drilled in it.The receiver has a fairly wide field of view, and to use it as an object detector you need to get this FOV down to a very narrow view.If you shroud both, the orientation of the two shrouds will have to be properly aligned with each other to allow the reflection off the IR LED to hit the IR receiver.